My neon 5.12 currently uses Plasma 5.12.5 and Frameworks 5.46
While xinput lists my Logitech K400 Plus keyboard and it's listed in /proc/bus/input/devices
my touchpad settings give a red letter message of "No touchpad found"
after some hours of searching, I see that even with much earlier versions of Plasma that this was being reported...

My question is... are there users out there who do not have this message?
i.e. when they select the touchpad app, they are able to enable/disable this input device!

This would help--those who still have this issue--to at least know that this isn't as much a KDE issue as much as it could be a driver issue
I say that because lspci does not list a kernel driver handling this specific device
Any other thoughts/input...?

Unfortunately I can only say me too.
I have a Logitech K400r, and have a similar problem: touchpad works just fine as mouse input but isn't recognized as a touchpad in system settings.

In my brief googling, I saw some stuff about using Solaar to interact with some of the features of the keyboard. I tried it and gotten it to work-ish; it seems I have to remove and reinsert the dongle in order for solaar to be able to properly interact with it (there's probably some permissions somewhere that I still need to sort out or something). However, even with that working right System Settings still doesn't believe that I have a touchpad.

It is not a plasma thing, it is because the trackpad on that keyboard is actually a mouse, in terms of how it is connected to the computer and the signals it sends to the kernel.

claydoh wrote:It is not a plasma thing, it is because the trackpad on that keyboard is actually a mouse...

Aaah... sounds reasonable!
Thank you for that...
now if only this "mouse" could middle-click and wheel scroll ...!